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wtf? thats not even really above the rear "strut tower"lol or shock tower.... thats off in the wheel well baby! i think it does nothing sry.... only real way to connect rear shock points is with a cage/welding a brace where the seats are connecting at the upper shock mounts or doing something like i did above the gas tank.
its not pretty but its painted and cleaned up. made of 1"x1"x.125" square tubing and is welded to the sides of the rear spring perches AKA shock mounts. it is completely hidden and cant be seen even when under the car and doesnt affect the gas tank at all. it ties the rear subframes/shock points together perfectly. it also ties in the gas tank support frames and floor togther... its the best design ive ever seen as far as functionality/strength. i also have a 6pt cage welded in also.
pic is the one side but its basically just a mirror reflection so u get the jist
wtf? thats not even really above the rear "strut tower"lol or shock tower.... thats off in the wheel well baby! i think it does nothing sry.... only real way to connect rear shock points is with a cage/welding a brace where the seats are connecting at the upper shock mounts or doing something like i did above the gas tank.
its not pretty but its painted and cleaned up. made of 1"x1"x.125" square tubing and is welded to the sides of the rear spring perches AKA shock mounts. it is completely hidden and cant be seen even when under the car and doesnt affect the gas tank at all. it ties the rear subframes/shock points together perfectly. it also ties in the gas tank support frames and floor togther... its the best design ive ever seen as far as functionality/strength. i also have a 6pt cage welded in also.
pic is the one side but its basically just a mirror reflection so u get the jist
Are you practicing welding on your car? Might want to practice some more on scrap metal first, those welds are horrible, no offence intended just being honest.
Last edited by Twin_Turbo; 02-05-2009 at 10:17 AM.
yea those welds are pretty nasty but i dont really care. they are solid. they just look bad bc i had to fill it up in sum spots.... its tough hacking those gas tank supports under the car in that lil @ss space where the tank used to be when its snowing out. they are solid and wont be seen so i dont really care. i was also using a cr@p chicago electric 105amp mig without the reverse polarity so its impossible to weld upside down.
everything that matters i TIG on the car anyways, just use the mig on sheetmetal stuff for repairs. believe me it'll hold. the end of the bar was TIG'd to the plates tho
Hate to break it to you guys but those braces dont do anything for our cars
Front shock tower braces do plenty because the weight of the front presses up on the towers forcing them to flex in/outwards
The rear shocks are under no such loads and do their only job of shock absorbing. The rear weight doesnt affect the area either because the springs are perched right under the rear frame
The only reason to add metal down there is around the shock mount points when converting to rear coilovers. Still no brace is needed as the gastank "hump" is firmly attached to the points and is very thick. An added brace is redundant weight
Hate to break it to you guys but those braces dont do anything for our cars
Front shock tower braces do plenty because the weight of the front presses up on the towers forcing them to flex in/outwards
The rear shocks are under no such loads and do their only job of shock absorbing. The rear weight doesnt affect the area either because the springs are perched right under the rear frame
The only reason to add metal down there is around the shock mount points when converting to rear coilovers. Still no brace is needed as the gastank "hump" is firmly attached to the points and is very thick. An added brace is redundant weight
Right on. That Brace, and all of those welds you've done is pretty much useless... Sorry. Unless you have rear coilovers, or a rear engined car...
heres a thread on someone who did the same thing. a rear mounted shock tower brace. he reported that it took away the T top rattles etc.... hmmm seems like the same thing SFC connectors do! unless u wanna say that SFC dont strengthen the car?
its understood that the rear shock towers dont see as much force or the same weight as the front end. easy is the weight diff but so is the springs. rear spring are 100-200lb usually so they dont see as much force as a 700lb front spring. but its easy to say that rear end flexes or calapses alil bit.
our TQ arm setup rear suspension has LCA, panhard rod, and TQ arm as the mounting... and all three see Different forces acting on them when the car is launched,braked, and turned. GM noticed that the panhard rod saw ALOT of force to keep the rear planted correctly when the car is turned, which is why GM incorportated the panhard bar "brace" that is the other bar which attaches to the same point as the panhard rod bracket on the rear subframe. That bar reinforces the panhard rod MOUNT as well as the rear subrames. much like a STB. go look for yourself, it bolts to one subframe and runs to the brace where it is bolted above the panhard bar/mount.
this has been accomplished many ways. even BMR makes a stronger tubular bar. and allows the use of dual exhaust over the rear end. Some ppl make the bars seen in this thread above the carpet, i made mine much like a thru floor subframe. but others incorporate them into the ROLL CAGES. which is essentially what a roll cage does AKA the "hoop bar" connects both sides more rigidly. so u could call mine more of a support than a brace.
third pic is of a cage that shows this kind of brace worked into the cage... but the pics i have i cant find. same idea but was right above the carpet and attached the 2 rear bars of that cage that attach at the shock towers together with roll cage tubing. same thing as the cross bar on the hoop.
hey go figure... i mean anyone whos installed them as noticed a POSITIVE difference... but there prob all lying right?
i say if u havent done it then dont say anything. if u have and it didnt make a diff then say it. theres a few ppl saying that "most of u" dont kno wat ur talking about
Last edited by customblackbird; 02-09-2009 at 03:21 AM.
Just speaking up for those of us who "dont know"...
Two of those links are from the same person...the second one just being a thread about the other threads...
Now...couple things here. That was a CONVERTABLE. And what he installed was more of a harness bar. I can honestly say I believe he felt a difference with that. Its a vert.... Any type of reinforcement bar would make a decent different. If you added b-pillars and a solid roof...it would feel even stiffer
On a t-top car, with SFCs, and all the other proper chassis upgrades, I dont think you'd notice a difference. I think it'd be even less on a hardtop. Placebo effect is a strong illusion.
BUT...with that said, I dont want you to think Im saying dont do it. You'll never read something from me saying what you do your car is a waste of time or is crap. I dont think inside the box and neither should anyone else. I know theres a few things on my ride that some would think isnt making a difference. Thats what the hobby is about. What you did to your car is fine. These old unibody's wont suffer from some extra metal here and there, thats for sure. Im just saying I dont think a rear brace lends itself to as much improvement as upgrading front end parts. So kudos to those of you messing around with this...and if there was something conclusive about stiffening the rear of these cars, Ide probably be inclined to try it. why not...especially if you fab it yourself.
Your best upgrades for the rear are tubular parts and good rear shocks, new bushings etc etc. That'll suffice for most thirdgenners no matter what they are doing with their cars.
Happy Modding!
J.
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Last edited by ghettocruiser; 02-09-2009 at 10:12 AM.
seriously, how can anyone that owns one of these cars say that the stock subframes are adaquit, when it consist of layers of 18ga steel and practicaly glued together, and a few spot welds. imo, there is no reason to flame someone that goes the extra yard to stregthen there car.
Last edited by iroc a 86 berli; 02-09-2009 at 10:56 AM.
seriously, how can anyone that owns one of these cars say that the stock subframes are adaquit, when it consist of layers of 18ga steel and practicaly glued together, and a few spot welds. imo, there is no reason to flame someone that goes the extra yard to stregthen there car.
Two questions for you. 1) who here is flaming? I see a fairly civilized discussion going on here. The word flaming gets thrown around as much as "scammer" does on the bad sale threads. 2) Who in here said the stock subframes are adequate? Everyone that owns an f-body realizes where the weaknesses are, and usually takes good measures to help the situation.
The 18ga glued together steel bodies must not be doing too bad. There are plenty of guys running these cars hard with minor mods...and guys running them even harder with full on race set ups. Knowing what to mod, and how to mod goes a long way with these things...just like any car.
Also...we shouldnt get confused on the difference between "rear strut tower brace" and "reinforcing the rear subframe". One infers a bolt in type of part. The other infers structural mods like welding in steel. Like customblackbird did. Im fairly interested in seeing results from either or...
If we have a nice tech discussion...we should end up with some good info in threads like these
J.
Last edited by ghettocruiser; 02-09-2009 at 12:37 PM.
agreed, i suppose there isnt technically any flaming. i realize this thread is about a bolt on strut conector, wich i dont see any real advantages in, but i have not experienced it myself. i was mainly refering to this comment from tice towards customblackbirds welded in brace. suppose i should have quoted tice.
Quote:
Originally Posted by Tice
Right on. That Brace, and all of those welds you've done is pretty much useless... Sorry. Unless you have rear coilovers, or a rear engined car...
haha..yeah I wasnt sure if you were saying I was flaming or what. Thanks for clarifying. I agree a little more tact could have gone into the weld critique.
I have some time tomorrow while Im at work. Ive got a guy here that did some work for GM as an engineer...I think I might have a conversation with him. He's rather old school, so I doubt he'll have much input. But Im pretty limited on structural numbers crunching.
haha...this is my idea of fun when my car is tucked away for the winter. Desk top fabbing and engineering.
Now does it do anything? Thats not proven yet but it can't hurt.
Some said it does nothing as its so strong back there but the same said when I cut a hole for a FP access door that the car would fall apart as it so weak back there.
I got them front and rear.
Twas cheap, looks trick if it does anything or not.
Biggest improvemnt I saw was when I gutted it and rewelded all the body pannels, them cheesy spot welds suck. Also cleaned all the goop out of the floor pan to side walls and welded it full length. Allot less flex.
No sub frames yet. But rear stock stuff has been boxed. LCA's & panahard bar. Handles like its on rails.
See sig link for hatch pics.
__________________ 86 Pontiac Firebird [68 Firebird HoodScoops, Notchback, Rear Mounted Tach, Inverted Wing,
T/A HoodVents in SailPanel, Front & Rear STB, Boxed LCA/PanHard, Fulley Welded Interior, Alston SFC] http://www.thirdgen.org/techboard/v6...-all-over.html
See link for newer pics and above mods.
seriously, how can anyone that owns one of these cars say that the stock subframes are adaquit, when it consist of layers of 18ga steel and practicaly glued together, and a few spot welds. imo, there is no reason to flame someone that goes the extra yard to stregthen there car.
have you ever looked at the rear frame rail? I cut mine all apart when i did my mini-tub job, and there is quite a bit of ~11ga metal in there. The rails are strong as hell, maybe a little weak where they go under the car, but this rear brace will not do anything.
The front strut towers are just that, towers, and they flex inward during suspension compression. The STB ties the two together so they cannot flex inward. The rears are part of the rear frame rails, and will not flex inwards, there is metal inbetween them, aka the floor, and that big hump behind the rear seats, where will things flex? Besides, there is a chassis brace, upper panhard bar, in the rear of the car that holds things together as well.
If anything, there may need to be more bracing from the "hump" behind the seats, in the shock mount/sring pearch area, to the floor area behind the doors. And a cage would preform this.
Last edited by //<86TA>\\; 02-10-2009 at 07:48 PM.
have you ever looked at the rear frame rail? I cut mine all apart when i did my mini-tub job, and there is quite a bit of ~11ga metal in there. The rails are strong as hell, maybe a little weak where they go under the car, but this rear brace will not do anything.
The front strut towers are just that, towers, and they flex inward during suspension compression. The STB ties the two together so they cannot flex inward. The rears are part of the rear frame rails, and will not flex inwards, there is metal inbetween them, aka the floor, and that big hump behind the rear seats, where will things flex? Besides, there is a chassis brace, upper panhard bar, in the rear of the car that holds things together as well.
If anything, there may need to be more bracing from the "hump" behind the seats, in the shock mount/sring pearch area, to the floor area behind the doors. And a cage would preform this.
very familiar with the guts of are chassis's. i dont recall a whole lot of 11ga in that particular area. really cant think of any sheet metal in these cars besides the k member thats 1/8in or "11ga" steel, but whatever dude, im done with this thread.
Im with Iroc a 86 berli on this one. i have yet to find anything thicker than maybe 14-16gauge on these cars. besides kmember/trans crossmember. if i had a choice and money and time i would rip all of the subframes off the car and build a tubular chassis.
the only area that i see that is strong is the area right above the rear spring/shock mount. thats the "beefiest"(sandwiched 14gauge steel) area. which is why i attached my rear bars of my cage to it. but i still have to argue that the "floor" is not adequate to tie them together for strength. the floor is 22gauge. i push on the part right above the gas tank it u can hear it POP in and out, same goes for right behind the rear seats. thats frigin ridiculous! even the gas tank supports are just 20gauge bent like a U and spot welded to the floor. i know bc i hacked through them remember!
with that being said, the rear spring mount/shock area is the only area thats sumwhat "boxed" to form an actual frame rail... other wise its just U shaped and spot welded to thin @ss 20-22gauge steel like the floor and rest of the subframes. so thats still very weak. esp the front subframes... that SHlT is just scary. the only reason these cars have "survived" is that they flex so D@MN much they they dont break, the flexing absorbs the forces.
the rear springs arent strong enough to flex inward but doesnt mean they dont TWIST, which it does which is why we install SFC, and cages to help reduce this. what i did was take a proven design(thru floor subframes, considered to be the strongest) and incorporate that so it "ties" the rear subframes together, limits twisting motion (being welded to floor) and effectively reinforces the shock/spring mounts as well as box the rear bars of my roll cage. i basically just reinforced my cage while attaching the rear spring mounts like a strut brace does. killed 2 maybe even 3 birds with one stone. same idea s X bracing the rear cage bars or adding a support bar right above the carpet to attach the 2 rear down bars of the cage.
ghettocruizer... i took that quote as flaming what i did. wrong wording.
Last edited by customblackbird; 02-11-2009 at 05:20 AM.
welding a cross-brace on the rear subframe like customblackbird did isn't bad at all... but that bar that someone bolted to the rear seatbelt retractor mounts is just silly. It's not serving any function.. there are no inward or outword forces acting on the wheel wells!
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Could you measure from the back of the drivers seat to the shock tower brace? I'm thinking it could serve as the shock tower brace, but also as a harness bar. I would think it would be strong enough... right? Also, could you provide a picture of how nicely it tucks against the giant hump. Does the rear seat easily latch into place, or is force required?
Thanks,
Mike
__________________ Suspension - far from stock, Brakes - far from stock Drivetrain - upgraded, Engine - bolt ons
I'm talking about the hump that the rear seat is against... Where the rear end moves under.
You make some good points... What if I made my own bar out of some thick walled rectangular steel tubing? I say rectangular so it fits better behind the seat when it is up. A wrap around harness will work with rectangular tubing, wont it? The main thing I'm worried about is the mounting location. Are these shouck mounts strong enough to deal with these forces or will I have to weld in some metal plates? If so, how thick should they be? Would mounting it at the height of the shock towers be an ok angle for the shoulder straps, or would I have to make brackets to bring it up higher? (I don't have my car out of storage yet so it is hard for me to visualize it)
if you were to make sumthing for the rear seat belts to anchor too it would have to be thick... is day at least .133 or something like a roll cage tubing size... they could sonic check the thickness and 1/8 is .125". and im sure it would have to be tubing not square stock. also the rear seatbelt bar has to be a certain angle from the seaters shoulder height. cant be too high or too low. thats another rule of the NHRA
my brothers crossbar/harness bar for his 68 vette is 1 5/8 or 1 3/4 roll bar tubing and is bolted to the car in some way. had the same loops for the harness as mine to locate it on the bar.
I've been modeling this in my drafting class at school and I've been putting it through a stress analysis. I'm trying all kinds of sizes and shapes, but it seems as though I may be going with a solid mild steel rectangular bar instead of a mild steel rectangular tube. I know it will weigh a lot more, but if that's what it takes to get what I want, so be it (the solid bar would be about 15 lbs as to 8 lbs for a tube).
I don't care if it meets NHRA requirements because my car will not be reaching the needs of a roll bar/cage any time soon. I only want this for SCCA autocrossing. I couldn't find any specs that it would have to meet for the SCCA, so I guess I'll just make it so I feel comfortable with it. I never even reach speeds of 60 mph on the courses and the only things to hit would be a light pole (very very unlikely) and a curb (I doubt I will see much force from that). THIS WILL NOT BE USED ON THE STREET OR ON A ROAD COURSE. I really only need it to hold me in the seat under braking forces.
My plan was to have it connect by the shock mounts (this would stay in permanently) and then have removable braces going the the main bar to the front seat belt mounts by the center counsel (only put in when I'll be using the bar). I figure if those sorts are good enough for GM to mount a seat belt, they should be good enough for a harness bar.
Mike
Like I said, this is just ideas in my head. I don't have my car out of storage yet so it is difficult for me to visualize this and see if it would even work.
not sure how u would get the bar from the top rear shock mounts on the hump to the back of the front seats for the harness mounting. thats about 2-3' distance. from the top of the hump to the back of the seats.
stephen..... didnt see the 3.2.2 section. saw a 3.2 section on saftey restraints
hey sorry guys to but in, but if you look at the structural assembly in the rear of our cars, a rear strut/shock brace don't do a roll of beans for our cars.
true but the cars still twist. and the only way to stop that is to conect the 2 sides of the subframes together.. not bolted but welded. like the bar i did in the rear. same idea as a cage hoop.
yea 3.3 and 3.3.2 read them before. thanks for the link
Thanks Stephen, but I already saw that. It only mentions roll bars and cages. Nowhere in the rule book does it mention anything about specifications for a harness bar.
I don't really care if it doesn't do much for strengthening the shock towers. I just want it to act as a harness bar. Strengthening the shock towers would just be a bonus if it happens. I know the braces going forward are going to be long, but where else can I brace it? I also understand it won't be lightest thing in the world, but if it fits where I want it to, it is safe, and it doesn't look like crap, I'm happy.
I figure three grade8 bolts by each shock mount and then the bracing by the front seat belt should be ok.
Mike
Oh, is there a company that sells just the shoulder straps in a long enough length for this to be possible? I already have 2 latch-n-link harnesses but the shoulder straps are going to be too short for this.
Do you guys think that welding in the bar like customblackbird did would allow you to eliminate the panhard bar support for better clearance of dual exhaust? it seems that you are accomplishing the same thing by tying the 2 frame rails together.
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Do you guys think that welding in the bar like customblackbird did would allow you to eliminate the panhard bar support for better clearance of dual exhaust? it seems that you are accomplishing the same thing by tying the 2 frame rails together.
Nope....The panhard bar support is for the passenger side mount that hangs down. It hangs down so far, it needs the support bar that rides lower than the floor above.
mo
Right on. That Brace, and all of those welds you've done is pretty much useless... Sorry. Unless you have rear coilovers, or a rear engined car... 
